A robot fish in aquaculture for real-time monitoring of the whole water area was designed and a control system of robot fish was built to facilitate the monitoring of water quality and underwater fish activities. The three-dimensional spatial path tracking error model of the robotic fish was established in the Serret-Frenet coordinate system to realize the precise operation of the robotic fish and study the three-dimensional path tracking control of the robotic fish. Based on the LOS guidance law and Lyapunov theory， a fuzzy sliding mode controller was designed. The algorithm has the advantages of fast convergence speed and strong robustness. Finally， Matlab simulation was used to verify the effectiveness of the control algorithm proposed in this article. The results of simulation showed that the designed controller enables the robotic fish to realize three-dimensional path tracking control under the condition of model parameter uncertainty and unknown external disturbance， and its control accuracy and robustness are significantly better than those of conventional PID and sliding mode controllers.